Spiroacetal diamine-epoxide liquid as curing agent for epoxy resins

ABSTRACT

EPOXIDES REACT WITH SPIROACETAL DIAMINES OF THE FORMULA   (-CH2-O-C(-R)(-R&#39;&#39;-NH2)-O-CH2-)&gt;C&lt;(-CH2-O-C(-R)(-R&#39;&#39;-NH2)-   O-CH2-)   TO FORM A VISCOUS LIQUID WHICH IS A GOOD HARDENER FOR EPOXY RESIN INTERMEDIATES, IN THE FORMULA R BEING HYDROGEN, METHYL, OR ETHYL, AND R&#39;&#39; BEING ALKYL HAVING 1 TO 6 CARBON ATOMS. EPOXY RESINS CURED BY MEANS OF THE HARDENER ARE FLEXIBLE, COLORLESS AND TRANSPARENT.

United States-Patent US. Cl. 260-340.7 6 Claims ABSTRACT OF THE DISCLOSURE Epoxides react with spiroacetal diamines of the formula I HzN-R' o-ohg cm-o \R-NH2 to form a viscous liquid which is a good hardener for epoxy resin intermediates, in the formula R being hydrogen, methyl, or ethyl, and R being alkyl having 1 to 6 carbon atoms. Epoxy resins cured by means of the hardener are flexible, colorless and transparent.

This application is a continuation-in-part of our copending application Ser. No. 880,356, filed on Nov. 26, 1969, now Pat. No. 3,679,707, and itself a continuationin-part of our application, Ser. No. 560,067, filed June 24, 1966, and now abandoned.

This invention relates to epoxy resin compositions, and particularly to curing agents effective for curing such compositions at room temperature.

Polyamincs, acid anhydrides, polyamides and polysulfides have been used commercially heretofore as curing agents in epoxy resin compositions. The flexibility often required of the cured epoxy resins in coatings, adhesives and castings could be achieved by the use of polyamide and polysulfide curing agents, but only at the cost of reduced tensile and flexural strength in the cured resins. Moreover, full curing by means of these agents could be achieved only at elevated temperature. The cured resins lack full transparency and are not colorless.

We now have found that epoxy resin intermediates can be cured completely at room temperature to colorless and transparent resins having excellent flexibility without loss of mechanical strength by the use of certain modified spiroacetal diamines as curing agents. The curing agents of the invention are reaction products of epoxides with a spiroacetal diamineof the formula HzN-R/ OCfia CHaO R'-NH wherein R is hydrogen, methyl or ethyl, and R is straight or branched-chain alkyl having 1 to 6 carbon atoms.

The curing agents of the invention are stable and do not discolor in storage, during curing or after curing. They produce hard, tough, substantially colorless and transparent cured resins from all epoxy resin intermediates in present commercial use or otherwise available to us.

Spiroacetal diamine compounds of the above formula which have been used successfully for preparing the curing agents of the present invention include 3,9-bis(aminoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane,

3 ,9-bis(2-aminoeth'yl)-2,4, 8,10-tetraoxaspiro [5 5] undecane,

ice

3 ,9-diethyl-3,9-bis (Z-aminoethyl)-2,4,8,10-tetraoxaspiro- [5,5]undecane,

3 ,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro [5,5] undecane,

3,9-bis(4-aminobutyl)-2,4,8,10-tetraoxaspiro[5,5]undecane,

3,9-bis( 1 ,1-dimethyl-4-aminobutyl)-2,4,8, IO-tetraoxaspiro 5,5 undecane.

The spiroacetal diamine compounds may be prepared by the methods disclosed in the German Pat. No. 1,092,029 or the US. Pat. No. 2,996,517 wherein formyl nitrile and pentaerythritol are reacted in the presence of an acid catalyst, and the formed intermediate 3,9-bis(cyanoalkyl)- 2,4,8,lO-tetraoxaspiro[5,5]undecane is subjected to catalytic hydrogenation. They may also be prepared by reacting an aminoaldehyde acetal with pentaerythritol in the presence of an acid catalyst.

The curing agents of the invention are prepared by heating a mixture of the spiroacetal diamine with an epoxide with or without a solvent inert to the reactants. Suitable solvents include methanol, ethanol, butanol, benzene, toluene, xylene, dioxane, ethyleneglycol monomethyl ether, ethyleneglycol monoethyl ether and the like. Heating is continued until a homogeneous viscous liquid is obtained after removal of the solvent, if any. The reaction temperature is preferably above the melting point of the diamine and below the boiling point of the epoxide so that the mixture is liquid. Temperatures between 20 C. and C. are usually satisfactory, and the time required varies inversely with the temperature.

It is preferred to use more than 0.25 mole of spiroacetal diamine per oxirane mole equivalent of the epoxide in the reaction mixture, but as much as 10 moles of spiroacetal diamine may be employed. A curing agent prepared with less than 0.25 mole spiroacetal diamine per oxirane mole equivalent of the epoxide does not completely cure an epoxy resin because of inadequate cross-linking, and the partly cured resin has poor chemical and mechanical properties. When more than 10 moles of spiroacetal diamine are employed in preparing the curing agent per oxirane mole equivalent, the diamine, which remains partly unreacted, crystallizes sooner or later and impairs the workability of the cured plastic.

The reaction between a spiroacetal diamine and an epoxide having one oxirane group produces a reaction mixture in which several of the compounds listed below can be found, the prevailing compound or compounds being determined mainly by the initial ratio of spiroacetal diamine NH X-NH and epoxide Y-CH-OH:

wherein X is spiroacetal and Y any of various radicals attached to the oxirane group:

More complex mixtures are obtained by the use of epoxides having more than one oxirane group. Even reaction mixtures prepared from equimolecular amounts of spiroacetal diamine and epoxide do not yield a single condensation product, but a mixture of reaction products which is a viscous liquid at ordinary temperature (20 C.), a fact believed to be essential for the beneficial effects of the curing agents of the invention. The various curing agents of the invention referred to hereinbelow have viscosities of approximately 1000 to 500,000 centipoise at 20i1 C. when determined cosimeter of the Brookfield type.

The reaction product may be subjected to fractional distillation to remove solvent or an excess of spiroacetal diamine if present, but small amounts of solvent or unreacted diaminedo not normally interfere with the normal curing action, and need not be removed. 1

Best results are generally obtained with curing agents prepared from 0.5 to 6.0 mole spiroacetal diamine per oxirane mole equivalent of epoxide.

The curing agents of the invention are colorless and transparent. Theydo not irritate the skin upon contact. No discoloration of the curing agents has been observed in three months of storage at room temperature. Storage for more than two months at temperatures below 5 C. did not cause unreacted spiroacetal diamine to crystallize nor otherwise to precipitate.

Representative epoxy resin intermediates capable of being cured by the curing agents of this invention are those based on the glycidyl ethers, of polyhydric phenols, such as 2,2-bis(4-hydroxyphenyl)-propane, resorcinol, hydroquinone, pyrocatechol, saligenin, 4,4-diphenylhydroxybiphenyl, l,S-dihydroxynaphthalene, dihydroxydiphenylmethane, dihydroxydiphenylsulfone, and on the glycidyl ethers of polyhydric alcohols, such as ethylene glycol, propylene glycol and glycerin.

The required amount of curing agent is determined by the number of active hydrogen atoms in the curing agent employed, and the number of oxirane groups in the epoxy resin intermediate. In general, it is preferred to use equivalent weights of spiroacetal diamine condensates and epoxy resin intermediates. However, the properties of the cured resin are not significantly affected by variations of not more than 20% in the amount of the curing agent.

The epoxy resins cured according to this invention are superior to resins produced from the same intermediates by means of conventional curing agents by a combination of better flexural properties, higher impact resistance, and better thermal shock resistance with equal or superior tensile strength and hardness.

The epoxy resin intermediates can be cured completely at room temperature to colorless and transparent resins having excellent mechanical properties. Heating is unnecessary, but may be resorted to for obtaining maximum strength in a shorter time. Even when cured at elevated temperature, the cured resins are not stained by the curing agents of this invention.

means of a vis-- i The curing agentsare corripatibleiwith all .cohventional fillers, diluents, reinforcing agents, pigments and other "'processin'g'aglits, such as flowcontrol additivesandaccelerators, so that resin compositions may be formulated according to the intended application in the usual manner.

The following examples further illustrate the present invention, but it will be understood that the inv ention is not limited thereto. r

EXAMPLE 1 was added drop by drop over a period of two hours, and the mixture was kept at the same temperature for one hour longer. A colorless and transparent, viscous, liquid mixture of the reaction product and of unreacted ATU was obtained. When stored below 5 C. for 24 hours and for three months at room temperature, the mixture did not form a precipitate.

The same procedure was used in preparing other curing agents from diamines and epoxides as listed in Table 1. Cardura E is a commercially produced glycidyl ester of a tertiary fatty acid of the formula having a molecular weight of 240-250, a boiling point of 135 C., R R R are aliphatic chains, and the total number of carbon atoms in the acid moiety of the ester is 9 to 11. Epon is a registered trademark for various glycidyl ethers of bisphenol A and its polycondensation products, all of which form curing agents with the spiroacetal diamines of this invention and will be described more fully hereinbelow.

TABLE 1 Mole ratio Viscosity diamine/ 0 0., cp Epoxide epoxide Brookfield Phenyl glycidyl ether 2:1 52, 000 Allyl glycidyl ether 1 1 13, 000 2:1 4, 200 1:1 7, 400 2:1 4, 400 1:1 37, 000 2:1 8,900 2:1 20, 000 2:1 10, 000 Phenyl glycidyl ether 2:1 49, 000 n-Butyl glycidyl ether- 2:1 5, 000 --do 1:1 7,900 Propylene oxi 1:1 7, 500 .do 2:1 15, 000 Hexylene oxide 1:1 14, 000 o 5 2:1 4,200 Styrene oxide. 1:1 380, 000 do 2:1 44,200 p-Pentadecylphenyl glyc dyl ether r 1. 2:1 14, 500 do 2.3:], ,300

1 3,4epoxy-6methylcyclohexylmethyl 3,4-epoxy-fi-methylcyelohexanecarboxylate.

1 3,9-bis( i-aminobutyl)-2,4,8,10-tetraoxaspiro[5,51undecane. v

3 3,9-bis(Z-aminoethyl)-2,4,8,10tetraoxaspiro[5,5lundecane.

4 3,9-bis(2-a1ninoethyl)-3,9-diethyl-2,4,8,10-tetraoxaspiro[5,5]undecane.

5 The hexylene oxide employed was a mixture of the terminal and inner epoxldes and was reacted with the ATU at C. for three hours.

r EXAMPLE2 11 H The curing agents listed in Table 1 were mixed with Epon 828 in the weight percentage ratios listed in Table 2 (grams curing agent per 100 g Epon 828) ,and 50 g. j

batches of the several mixtures were stored in identical containers in an air-conditioned room at 20 l C. and 65% relative humidity. For comparison, two batches of Epon 828 were mixed with conventional, typical polyamine and polyamide curing agents respectively in the ratios recommended. The polyamine was triethylene .tetramine (TETA), the polyamide curing agent a commercial product whose precise composition is not known (Tohmide 245 and which has an amine value of 400. The pot lives in minutes and maximum exotherms of the mixtures are listed in'Table 2.

.Resin specimens prepared from the batches described in Example 2 were subjected to heat distortion tests (ASTM D648-56) and flexure tests (ASTM D790-63),

and the curing conditions and test results are listed in Table 3, wherein R.T. is room temperature, all other temperatures are in C., and HDT is heat distortion temperature. N failure under the available test conditions is indicated by r. EXAMPLE4 Test specimens were prepared from 80 g. each of compositions listed in Table 2 by curing the mixtures in cylindrical molds 01-70 mm. diameter and 30 mm. depth together with a spring washer of one inch diameter at room temperature for 14 days. They were then tested for thermal shock resistance by up to ten cycles of alternating immersion in boiling water and in ice water for periods of 30 minutes, and inspected. The results are listed in Table 4 in which the ratings have the following meaning:

ANo cracks B-Slight crack C-Small crack D--Considerably cracked E-Large and numerous cracks +-Cracked during curing Where more than one line is associated with a curing agent, more than one specimen was tested. No. 7A differed from No. 7 in Table 2 by the use of 70% curing agent (15% excess).

TABLE 4 Number 0! cycles Curing agent 1 4 5 6 7 Tohmide 245 EXAMPLE 5 Epoxy resins prepared by curing mixtures of the invention described in Example 2 at room temperature for 14 days were machined to test bars 15 mm. x 15 mm. x mm. having a transverse semicylindrical notch of 1 mm. radius in the center of one of the elongated rectangular TABLE 3 Strain max., Strength, Modulus, Curing agent Curing conditions mm. kgJmm. kg./mm. No. 1 Roomtemperature.....- 80 31.3 14.4 388 3 hours/80 75 29. 2 12. 2 298 gifiom tigrperature 20. 0 g ours Room temperature 75 11. 0 290 3 hours/80 77 29. 6 11.0 287 $9 738 it it? 583 ours Room temp 52 21.6 10. 0 295 3 hours/120 75 11.5 313 Room temperature 58 34. 2 1 10. 5 320 3 hours/100 10. 7 310 a /sa a at a: as

ours Room temperature 60 25.0 10. 1 250 Room temperature 29. 5 12. 0 320 11 t:s 38 22-2 as as ours No. 12 Room temperature 65 29. 1' 11.1 300 62 22. 2 12.7 p 379 87 16. 2 12.4 298 60 25. 2 10.8 292 66 17.3 11. 1 295 68 20. 5 11.2. 305 81 18. 3 10.3 v 310 60 25. 7 11. 2 301 R it 2-2 11 :22

oom em era ure.. TETA "is hours/l0 Q 79 15.6 13.1 320 Tohmide 245-... 3 hours/65 64 20. 7 9. 85 242 faces. The notched specimens were subjected to Sharpy impact resistance tests according to Japanese Industrial Epon 828 was chosen in all preceding examples as the resin intermediate for demonstrating the superior me- Standard K-69-11. Mean values of six tests are listed in Table 5. The capacity of the apparatus. usedwas15.7 kg.-cm./cm. and values of l5.7+ in the table indicate that the specimen did not fail. Comparison tests were run with a mixture prepared from Epon 828 and 9% TETA cured 14 days at room temperature, and with a mixture of Epon 828 with 50% Tohmide 245 cured at 65 C. for three hours.

The mixtures described in Exmaple 5 were cured in a glass mold at 120 C. for 30 minutes to prepare resin sheets from which tensile test specimens were machined to the specifications of Japanese Industrial Standard K-6911. The specimens were tested for tensile strength and modulus of elasticity in tension at 21 C., RH. 65%, at a cross-head speed of 5 mm./sec. Mean values in kg./mm. of the results obtained with 3-6 specimens are listed in Table 6.

TABLE 6 Tensile Curing agent strength Modulus EXAMPLE 7 Epon 828 was mixed with ATU (35%), curing agent No. l (60%), No. 2 (60%), No. 3 (50%), TETA (10%) and Tohmide 245 (50%). The several mixtures so prepared were cured as indicated in Table 7 and subjected to fiexure tests under the conditions of Example 3. While comparable values for maximum strength and elastic modulus were recorded for the tested resins prepared with curing agents of the invention and ATU alone, the resins cured with the agents of the invention were superior in their values of maximum strain before failure to the specimens cured with ATU alone and to those cured with TETA or Tohmide 245 under comparable conditions.

chanical properties of epoxy resins cured by means of the curing agents of the invention in order to facilitate correlation of the several sets of data. However, closely analogous results were obtained with all other commercially available epoxy resin intermediates which we have been able to test. Epon 828 is merely representative of the glycidyl ethers of bisphenol A, glycidyl ethers of the poly-condensation products of bisphenol A of the formula and mixtures thereof, which are useful both as reaction partners for the afore-mentioned spiroacetal diamines in preparing the curing agents, and as resin intermediates which may be hardened by means of the curing agents. In the formula, m is zero or an integer. I

Epon 828 is a liquid mixture of such ethers or ether polycondensation products which has an average molecular weight of approximately 380, a corresponding epoxy equivalent of 185 to 192 g. per gram equivalent of epoxide, and an esterification value of about 85. It is prepared by condensation of bisphenol A with epichlorohydrin as generally described in British Pat. No. 974,139. The commercially available product has a color of 8 max. (Gardner) and a viscosity of to poises.

Epon 1001, referred to in Table 1, has an average molecular weight of approximately 900 with a corresponding epoxy equivalent of 425-550, and an esterification value of 145. It is a solid melting at 65-75 C., a Gardner color of 4 max., and a viscosity of D-G on the Gardner-Holdt scale as determined in a 40% solution of the material in diethyleneglycol monobutyl ether at 25 C.

Epon 834 is a liquid which is intermediate in molecular weight (approximately 480), epoxy equivalent, esterification value and viscosity between the two epoxides described above, and has been used successfully as a reaction partner for the spiroacetal diamines and as a resin intermediate according to this invention.

The epoxides listed in Table 1 are merely representative of those which form viscous, liquid condensation products with the spiroacetal diamines described above. Analogous viscous mixtures of condensation products were obtained under the reaction conditions of Example 1 with the epoxides enumerated in Table 8 below, and tests indicate that they are as effective in curing epoxy resin intermediates at room temperature as the curing agents more fully described above. No viscous, liquid condensation products of one of the spiroacetal diamines defined above and of an epoxide have been found which would not show the desired curing effect. In the table, G is glycidyl and n is an integer greater than 3.

11. What is claimed is: 1. A liquid viscous at 20 C. and capable of curing a liquid epoxy resin intermediate at room temperature, 1, said viscous liquid essentiallyconsisting'of the product of condensation at 20 to 150 C. of a spiroacetal diamine of the formula 1' v I R o-oH, 0E

said spiroacetal diamine per oxirane group equivalent of said epoxide, in said formula R being hydrogen,

methyl, or ethyl, and R being straight or branched- 5 chain alkyl having 1 to 6 carbon atoms.

2. A liquid as set forth in claim 1 having a viscosity of 1000 to 500,000 centipoise at 20:1 C. as determined by means of a Brookfield type viscosimeter.

3. A liquid as set forth in claim 2, wherein said epox- 2 ide is a member of the group consisting of phenyl glycidyl ether, allyl glycidyl ether, n-butyl glycidyl ether, glycidyl ester of a tertiary fatty acid having 9 to 11 carbon atoms, 3,4-epoxy 6 methylcyclohexylmethyl 3,4-

epoxy-6-methylcyclohexanecarboxylate, diglycidyl ether 25 from epichlorohydrin and bisphenol A, propylene oxide,

1 r fglycidyl ether of .hydrfoquinonfd, CH1 GHQ-O 5N r.

12 hexylene oxide, styrene oxide; p-pentadecylphenyl glycidyl ether, n-propyl glycidyl ether, diglycidyl ether, diethyleneglycol diglycidyl ether, triethyleneglycol diglycidyl 'ether,-="butanediol diglycidyl ethen -glyceroldiglycidyl ether", polyethylene glycol diglycidyl ejthericresyl glycidyl ether, p-butylphenyl glycidyl eth dlgl d l ether'of re:

chol, triglycidyl ether of phloroglu' 'lc'i-n ,acryla'te, glycidylv ester of polymericfat y-aci guy ester of adipic acid, glycidyl ester of sebacic acid glycld u ester of phenolphthalin, 'cictyleneoxide, glycidyl eth ef ester of 2,4,6-tribromo-3-hydroxybenzoic acid, ethylene oxide, butadiene dioxide, .dirnethylpentadiene.-dioxide, ;dioxide of 4,6-diallyl-m-xylcne,"'divinylbenzene dioxide; vinylcyclohexane monoxide, vinylcyielohexane dioxide,."a pinene oxide, dipentene monoxidg, ,lilnonelne dioxide, epoxidized soybean oil,- epoxidined ow oil, -"epoxidiz ed lemon oil, and epoxidizedlanoline'oil.

4. A liquid as set forth in-claim 2,,wherein said-,epoxide is a glycidyl ether of bisphenol A.

5. A liquid as set forth in claim 2, wherein said epoxide is an alkylene oxide having 3 to8carbon atoms."

6. A liquid as set forth in..claim 2,.whereinsaid epoxide is a compound of the formula wherein m is zero or an integer.

References Cited UNITED STATES PATENTS 4/1964 McGary et a1. 260 -2 US. Cl. X.R.

260-2 BP, 2 N, 18 PF, 47 EN, 59

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent '77 Dated November 20, 1973 fl mimsnmumuh It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, after line l2, insert Claims priority; application Japan, June 26, 1965, 38175/65; February 9, 1966, 7496/66 Signed and sealed this 9th day of-April 19m.-

(SEAL) Atte st:

EDWARD M.FLETCHER,JR. C. MARSHALL ,DANN

9 Commissioner of Patents Attesting Officer USCOMM-DC 603764 69 u.s. GOVERNMENT PRINTING OFFICE I90 o-su-ssl,

F ORM PO-105O (10-69) 

